A hard disk drive (HDD) typically includes a rectangular housing, a recording medium (disk) disposed in the housing, and a magnetic head which reads/writes data from/to the recording medium. Further, the housing typically includes a rectangular base and a top cover formed in the shape of a plate and screwed to the base. When such an HDD is used in an external device, when an external magnetic field such as electromagnetic waves is applied from the external device to the housing of the HDD, noise may negatively affect operation of the HDD, i.e., data reading/writing by the magnetic head on the disk. It is therefore preferable that the HDD has capability to inhibit magnetic field resonance occurring because of an external magnetic field, and prevent the magnetic field resonance from interfering with its operation.